A girl is saying she slept with my bf. Theres no evidence and he denies it. Do i drop it? Shes persistant.?

Some girl tried to kiss my boyfriend ages ago, my bf told me about it, they were friends and he pushed her away and told her had a girlfriend. I know he pushed her away because he showed me texts on his phone from her saying sorry, etc. Anyway, he continued meeting and being friends with her and it really annoyed me because obviously she fancied him and wanted him to herself. She sent me a facebook message saying no matter what I had heard from people nothing further happened, because I was asking people who were there what happened. Me and my boyfriend went on a break after being together for two years, when a couple of months ago I bumped into this girl at a nightclub. She was really drunk and saying how she really liked him and I seem like a nice girl and that she may as well tell the truth. She said the night she kissed him he responded and things went further, and she said about a year after that they had , and my bf had told her we had broken up. She said she hasnt seen him in ages now and it was a "thing" that just happened once. She said she used to look at my pictures on facebook and think i was really pretty and get jealous. I thought that was a strange thing to say. Anyway I told my bf, I was in tears and he got so angry, confronted her on facebook so everyone could see, calling her an obsessive liar, who is jealous, etc. She replied saying hes a cheat, and he removed her as a friend saying he hopes he never sees her again. She told me when she was sober the next day she was telling the truth. I don't know who to believe, a few people I know have said shes a psycho and not to listen to her, while others say why would she make up such a lie if she now has a bf and hasnt spoke to my bf in ages? Theres no evidence to back her up so what do I do??? My bf now hates her and never wants to see her again, he says she really jealous and was always asking him if he thought she was pretty and how much he liked me. How do I get over this or know the truth?